This invention relates to spatially programmable electrode-type rolls for electrostatographic processors and the like and, more particularly, to magnetic brush development systems including spatially programmable electrode-type applicator rolls.
In a conventional electrostatographic printing process of the type described in Carlson's U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged imaging surface is selectively discharged in an image configuration to provide a latent electrostatic image which is then developed through the application of a finely divided coloring material, called "toner". As is known, that process may be carried out in either a transfer mode or a non-transfer mode. The non-transfer mode is characterized by the use of the imaging surface as the ultimate support for the printed image. In contrast, the transfer mode involves the additional steps of transferring the developed or toned image to a suitable substrate, such as plain paper, and then preparing the imaging surface for re-use by removing any residual toner particles still adhering thereto.
The Carlson patent specifically relates to xerography, which is probably the best example of the outstanding commercial success of electrostatography. Indeed, xerographic copiers and duplicators occupy an important position in todays business world. Xerography, of course, involves the use of a photoreceptor as the imaging surface, but there are other types of electrostatographic processors. For example, there are some wherein the imaging surface is a uniformly charged electrically insulating member which is selectively discharged non-photographically -- e.g., by appropriately controlled stylii -- to provide a latent electrostatic image which permits of subsequent processing in essentially the same manner as the photographically generated latent image of a xerographic processor. Moreover, it should be understood that xerographic and similar electrostatographic printing processes are not limited to use in stand alone copiers and duplicators. For instance, those processes have also been found to have utility in the facsimile art.
Electrostatographic processors conventionally rely on a multi-component developer comprising a mixture of toner particles and larger, so-called "carrier" particles. The materials for the toner and carrier (or, sometimes, carrier coating) components of the developer are selected so that they are removed from each other in the triboelectric series, whereby electrical charges of opposite polarities tend to be triboelectrically imparted to the toner and carrier particles. Furthermore, in making those selections, consideration is given to the triboelectric ranking of the materials to the end that the polarity of the charge nominally imparted to the toner particles opposes the polarity of the latent images which are to be developed. Thus, in operation, there are competing electrostatic forces acting on the toner particles of such a developer. Specifically, there are forces which at least initially attract them to the carrier particles. Additionally, the toner particles are subject to being electrostatically stripped from the carrier particles whenever they are brought into the immediate proximity of or actual contact with an imaging surface bearing a latent image.
Others have previously recognized that locally generated electrostatic fields may be advantageously utilized in electrostatographic processors to control or at least enhance the development, transfer and cleaning processes. Generically described, the imaging surface of such a processor is merely an electrically insulative layer having an electrically conductive backing. Thus, an electrostatic field may be generated simply by holding the backing for the imaging surface at one potential while maintaining an appropriately spaced electrode at another potential. Indeed, stationary electrodes are sometimes configured to generate relatively sophisticated fields. For example, there are development systems which include a stationary electrode having a plurality of electrically isolated segments so that individual segments of the electrode can be biased to different potentials relative to the backing for the imaging surface, thereby generating an electrostatic field which is tailored to accomplish several different functions, such as suppressing toner cloud emissions and reducing background development. Heretofore, however, rotating electrodes have not permitted of such sophistication. This is a serious shortcoming inasmuch as electrodes of that type are being widely utilized, especially in magnetic brush development systems.